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B A Streak plates incubated for 4 days at 26°C of Cryptococcus laurentii CAB 578 on Long Ashton decarboxylase agar amended with L-arginine and phenol red (pH indicator). Arginine decarboxylation, and hence potential polyamine production, was indicated by the change of phenol-red from yellow to pink (B). Control, without L-arginine, is depicted in A.